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Converter to Crank Pilot fit #2561212
10/09/18 01:09 AM
10/09/18 01:09 AM
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Mequon, WI
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gzig5 Offline OP
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Mequon, WI
On a 340 with a 727 TF, how much clearance should the end of the pilot on the torque converter have to the bottom of the pilot hole in the torque converter? Pulled the trans for rebuild and noticed the old converter showed that it was in contact with the bottom of the crank pilot hole. Chalked it up to bad tolerances. Now getting ready to put new converter in with rebuild 727. Pre-fitting the converter and it seems like the converter pilot bottoms out in the crank and there is space between the converter and the flex plate. Hard to tell in the car but looks like at least 1/16" clearance. Took some rough measurements and it is at least flush, if not bottomed out. That doesn't seem right. I would think that the converter would contact the flexplate before the pilot bottoms out in the crank.

I'm going to pull the flex plate and check it to the converter but wanted to ask what the clearance should be before I got into it.

Motor is internally balanced 1971 block. Trans is from a 1973 car and it had an externally balanced converter, which is incorrect for this motor. New converter has no weights. I got the car like this and it's not the first screw up I've found. Seems like the flex plate is incorrect but I can't figure out how.

Re: Converter to Crank Pilot fit [Re: gzig5] #2561237
10/09/18 02:17 AM
10/09/18 02:17 AM
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Mequon, WI
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gzig5 Offline OP
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With the flexplate removed and measured on the bench I get 0.175" from the crank face to the other face of the flexplate that contacts the converter. 0.265" from the end of the converter pilot to the mounting blocks and 0.400 for from the crank face to the bottom of the hole. .175 + .265 = .440" from the crank face to the end of the pilot which is longer than the .400" depth of the hole so if my math is right, the flexplate is being compressed 0.040" with the converter bottomed out in the hole. Does that make sense? Something wrong or is that how it was designed?

One wing of my flexplate is bent a bit too which isn't helping. It is obviously not original to the motor because it has blue paint on it which doesn't match the red/orange on the engine. I'm pretty sure the motor was from a manual trans car (has the bronze bushing in the end of the crank) and they would have needed an automatic flexplate when they joined the engine to the trans. So, is it possible they got one from the wrong car? It has the offset bolts on the crank.

IMG_1715.JPG
Last edited by gzig5; 10/09/18 02:21 AM.
Re: Converter to Crank Pilot fit [Re: gzig5] #2561300
10/09/18 09:36 AM
10/09/18 09:36 AM
Joined: Jan 2003
Posts: 6,363
Abilene, Texas
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fastmark Offline
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Can’t help you with the interference but I can tell you that all the forged 340 cranks I have ever had, all had the bushing in the crankshaft pilot hole even if they were a original auto tranny equipped.

Re: Converter to Crank Pilot fit [Re: gzig5] #2561599
10/09/18 08:59 PM
10/09/18 08:59 PM
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Mequon, WI
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gzig5 Offline OP
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Crickets? Nobody can confirm spacing on the converter to the back of the crank? I've ordered a new flexplate and hopefully that will change something.

Re: Converter to Crank Pilot fit [Re: gzig5] #2561659
10/09/18 11:07 PM
10/09/18 11:07 PM
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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Bend,OR USA
The converter mounting bosses should contact the flex plate flush, no space or clearances at all tsk
How far back will the converter move before stopping? How much space is there between the flex plate now and the converter with the converter shoved all the way back into the pump ? scope


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Converter to Crank Pilot fit [Re: gzig5] #2561661
10/09/18 11:14 PM
10/09/18 11:14 PM
Joined: Jan 2003
Posts: 20,149
Park Forest, IL
slantzilla Offline
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If you can get the 'Search' function to work there was a thread in the race section last spring that had all the measurements you're looking for.


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Re: Converter to Crank Pilot fit [Re: gzig5] #2562112
10/10/18 08:24 PM
10/10/18 08:24 PM
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Posts: 350
Mequon, WI
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gzig5 Offline OP
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From everything I can find, there is only the six bolt and eight bolt flex plates so the I've got a standard 6-bolt flex plate for 10" pattern on order from Napa. Hopefully get here in the next two days.
I didn't take any measurements before I removed everything because I wasn't aware of the issue. With just the old flexplate and new converter, it would bottom out in the crank and there would be ~1/16" on either side, left to right. It was too difficult to tell top to bottom. But, I don't know if the L/R rock was on the petal that was bent. The transmission doesn't have any affect on how close to the crank the converter ends up, that is determined by the flex plate, so I will wait until I have the new one before trying again. I'm working by myself so maneuvering the trans onto the jack and up and in is something I hope to make a one time deal.

I'm wondering if I'm not chasing a ghost here, though. The "new" torque converter has a similar pattern on the end of the crank pilot as the old one I removed. As if it was in contact with the crank in its previous life. I think this converter may be rebuilt on a used case?? ProTorque brand.

I'll see if I can find that thread 'Zilla

Re: Converter to Crank Pilot fit [Re: gzig5] #2562461
10/11/18 03:05 PM
10/11/18 03:05 PM
Joined: Jan 2003
Posts: 25,618
Rio Linda, CA
John_Kunkel Offline
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As long as there is no air gap between the converter drive lugs and the flexplate with the converter pulled all the way forward, there should be no problem. Even if the converter snout was bottomed in the crank at the same time the drive lugs contact the flexplate, it wouldn't be a problem.


Same if the converter hub was only a few thou from bottoming out in the crank, the flexing of the flexplate could cause contact witness marks on the converter snout.


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Re: Converter to Crank Pilot fit [Re: gzig5] #2563527
10/13/18 07:36 PM
10/13/18 07:36 PM
Joined: Mar 2011
Posts: 3,056
Michigan
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Michigan
By design - all the old RWD converters are supposed to be bottomed out in the crank pilot.

All FWD designs are floating pilot which means they are not supposed to be bottomed out in need the crank pocket. They are called floating. When installing them you should apply a thin coat of lube to the converter point so it never rusts and allows it to float.







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